FIG. 13 is a configuration diagram of a conventional centrifugal fan 1. The centrifugal fan 1 is comprised of a main plate 2 that rotates, a shroud 3 which is provided so as to be opposed to the main plate 2, and which has an intake port 39 for taking in air, and plural blades 4 which are connected and fixed between the main plate 2 and the shroud 3. Some of the blades 4 may have a hollow structure 5 in the inside for weight saving. When the centrifugal fan 1 rotates in a fan rotational direction 6 shown by an arrow around an rotational axis 17, an airflow 7 is taken in from the shroud side, and the pressure of the airflow 7 is increased while the airflow 7 passing through the blades from a leading edge 41 (also called a blade leading edge part) to a trailing edge 42 (also called a blade trailing edge part), and the airflow 7 is blown outside. Here, a part of the shroud 3 is omitted to make the diagram easy to see.
FIG. 14 is a configuration diagram of a ceiling-embedded type air conditioner using a turbofan 1a. (a) of FIG. 14 is a diagram corresponding to a case wherein the turbofan la installed in a ceiling is viewed from below. (b) of FIG. 14 illustrates an X-X cross-section surface in (a) of FIG. 14. Both the turbofan la and a motor 10 that makes the fan rotate are included at a center of the inside of a unit that is made up of a top plate 8 and a side plate 9, and a heat exchanger 11 that exchanges heat with air is arranged in an approximately quadrangular shape so as to surround the turbofan la and the motor 10 in the periphery of the motor 10. A facing plate 12 that faces a room is arranged on a lower side of the unit, an air suction port 13 is placed at a center of the facing plate, and an air blow outlet 14 is placed around the air suction port 13, wherein a vane 15 that controls an airflow direction is installed. Air inside a room is heat exchanged by the heat exchanger after passing through the suction port and the fan, and is blown into a room according to a direction from the blow outlet to the vane, as shown by an arrow 16.
In recent years, efforts to reduce noise and save energy of a blower have been demanded, and there have been many ideas to realize them.
There is a technique to uniform a blow-off velocity distribution by gradually increasing a thickness of a lateral cross-sectional shape of a blade from a shroud side to a main plate side, and narrowing a distance between blades (Patent literature 1).
Further, there is a case example wherein by displacing (shifting) a junction position of a blade between a side plate and a main plate, and guiding a flow on the main plate side to the side plate side, a burble between blades is reduced, a wind velocity distribution is uniformed, and noise reduction is realized (Patent literature 2).
Further, there is an example wherein a blade surface on the main plate side and a shroud side is formed to slant in a rotational direction in order to uniform a wind velocity distribution in a direction of a rotational axis and decrease turbulent noise (Patent literature 3).